For your first feature, at about what age group are you looking to cast for?
50/50 is nice.
Love & Other Drugs wasn't too bad.
Brokeback Mountain and The Kids Are Alright might be a stretch for a debut project, but Transamerica ain't too bad.
AmeliƩ might also be a bit much.
Pecker.
For scifi-lite try Never Let Me Go.
Henry Poole Is Here and Bella are two of my goto fave little movies about relationships.
Before Sunrise and Before Sunset are worth watching.
Zack & Miri Make A Porno ends well.
Probably are some good reference films in this list, as well:
http://boxofficemojo.com/genres/chart/?id=romanticcomedy.htm&sort=date&order=DESC&p=.htm